This invention relates to a discoidal monolithic ceramic capacitor and more particularly to such a capacitor having at least one floating electrode and being suitable for use in high voltage circuits at high frequencies. Discoidal or cylindrical capacitors having coaxial terminals or leads are known to have good electrical properties at high frequencies and by extending the center lead in opposite directions away from the body, i.e. axially, this structure is particularly useful as a high frequency filtering feed-through capacitor.
In capacitors intended for use at high voltages, it is known to employ a floating electrode having an equal capacitive relationship with respect to two terminated electrodes. Such capacitors are in fact two series sub-capacitors, whereby the voltage across the dielectric layers is half that applied between the capacitor terminals. The dielectric stress can be reduced further by the employment of additional floating electrodes, effectively increasing the number of sub-capacitors in the series string between the terminals. Such floating electrodes always have a range of registration (mis-registration) positions with respect to the terminated electrodes due to the particular tools, controls, etc., that are a part of a given manufacturing process. In typical process steps for making monolithic ceramic capacitors it is not unusual for such electrode misregistrations to reach .+-.15%. In a series string of sub-capacitors, the capacitor with the lowest capacity drops the greatest voltage and is most prone to voltage breakdown. In the patent to Coleman and Lo, U.S. Pat. No. 3,896,354 issued July 22, 1975, and assigned to the same assignee as is the present invention, it is shown how the effect of such misregistrations in an X or Y direction may be essentially eliminated by providing the electrodes with oppositely disposed extended portions.
It is an object of the present invention to provide in a cylindrical monolithic ceramic capacitor floating annular electrodes having equal capacitive relationships with two other annular electrodes which equal relationships are essentially unaffected by electrodes misregistration in any direction.
It is a further object of this invention to provide a monolithic ceramic capacitor capable of high yields in manufacture and having seriesed sub-capacitors wherein the active dielectric layers experience a uniform voltage stress.